The present invention is directed to films, coatings and articles useful in packaging applications, especially in the packaging of oxygen-sensitive materials, such as foodstuff and medicaments.
Packaging articles, whether in the form of a film (single or multi-layer), or structural design which may be flexible, semi-rigid, rigid and which may be of a lidded or collapsible design ("Packaging Article"), serve not merely to contain the substance being packaged but, depending on the nature of the substance, to also prevent ingress of harmful matter from the environment or, alternately, of egress of volatiles within a Packaging Article.
Oxygen from the atmosphere has long been recognized as one of the most harmful matter for many packaged materials, especially foodstuffs. Thus, the teaching herein shall be mainly directed but not limited to Packaging Articles which have high oxygen barrier properties due to having, as part of the Article's structure, a hydroxy-functionalized, regio-regular hydrocarbon polymer. Packaging Articles which comprise subject regio-regular polymer having certain other functional groups, as described herein, provide Articles with other desired properties, as fully disclosed herein below.
In packaging oxygen sensitive substances, such as foodstuffs, beverages, and pharmaceuticals (collectively "products"), oxygen contamination can be particularly troublesome. Care is generally taken to minimize the introduction or concentration of oxygen or to reduce the detrimental or undesirable effects of oxygen on the foodstuff or beverage.
Molecular oxygen (O.sub.2) can be reduced to a variety of intermediate species by the addition of one to four electrons; these species are superoxide, hydroxy radical, hydrogen peroxide, and water. O.sub.2 and water are relatively unreactive. However, the three intermediate species are very reactive. Also, O.sub.2 can be activated to single electron state oxygen (which can undergo subsequent reduction to the more reactive oxygen species) by irradiation, or by the presence of catalytic agents. These reactive oxygen species are free radical in nature, and the oxidative reactions in which they participate are therefore autocatalytic.
Carbon-carbon double bonds are particularly susceptible to reaction with the intermediate species. Such carbon-carbon bonds are often found in foods and beverages, pharmaceuticals, dyes, photochemicals, adhesives, rubbers and polymer precursors. Virtually any product which has complex organic constituents will contain such carbon-carbon double bonds or other oxygen reactive components, and hence are susceptible to undergoing oxidative reactions. Thus, if the oxidation products adversely affect the quality performance, odor or flavor of the packaged product, then preventing oxygen ingress into a Packaging Article will greatly benefit the packaged products storage life and usefulness.
A number of strategies exist to deal with oxygen which is contained within a Packaging Article's free void space. The most basic is to remove the oxygen by vacuum or by inert gas sparging or both. More recently, oxygen scavenger compositions have been added to polymeric gasket compositions used in certain elements of Packaging Articles (e.g., bottle caps and can closures) as well as in one or more layers of polymeric films used to form Packaging Articles. Such scavenger compositions address the need to remove oxygen from the interior of a closed Packaging Article by reacting or combining with the entrapped oxygen or with oxygen which may enter the Packaging Article during transportation or storage. Although the methods and compositions described above address the concerns with entrapped oxygen, they do not primarily address the problems associated with entry of oxygen and other contaminants into a Packaging Article from the exterior environment.
Glass and metals provide packaging materials which have extremely good barrier properties with respect to the ingress of substances from the exterior environment. However, these packaging materials are costly, provide Packaging Articles which are heavy, rigid in construction and, in the case of glass, are breakable.
Polymers have also been used extensively in packaging applications where they have many advantages over the use of glass or metal. The advantages are derived from the diversity of polymers themselves in their mechanical, thermal, chemical resistance and optical properties and from the diversity and adaptability of fabrication techniques which can be employed. Thus, flexible bags, semi-rigid and rigid containers as well as clinging and shrinkable films can be made into Packaging Articles which have walls of homogeneous, laminated or coated structure.
Further, packaging materials and the articles may be formed of a single layer (one composition throughout its thickness) or as a multi-layer structure wherein different layers of the structure are present to provide a combination of desired properties. For example, one or both surface layers may be composed of polymer(s) having groups which provide sealing properties. Other layers may be formed of polymers having high tensile strength to impart tear resistance to the resultant film and article. Similarly, polymers or blends of polymers may be used in different layers of a multi-ply material to impart gas barrier properties, printability characteristics, strength, heat shrink properties, adhesion between other layers which otherwise have poor adhesion properties to each other, as well as other properties desired of the resultant Packaging Article.
It has been presently found that improved packaging materials can be formed by utilizing certain polymers which have functional groups capable of contributing a particular property and where the structure of the polymers have a substantially linear hydrocarbon backbone chain (is substantially devoid of side chains) and has a substantially uniform sequence of atoms along the polymer chains. It has been further found that improved packaging materials can be formed from certain linear polymers which have a uniform sequence of atoms along the polymer chain and have functional groups substantially uniformly pendent therefrom (regio-regular structure). It has been still further found that improved packaging materials can be formed from said regio- regular hydrocarbon polymers which have functional groups pendent from vicinal carbons along the chain (i.e., the functional groups are present in a head-to-head configuration).
Thus, it is the object of the present invention to provide packaging materials and Packaging Articles formed therefrom comprising a regio-regular, linear hydrocarbon polymer having a structure comprising pendent functional groups uniformly distributed along the polymer chain.
It is also an object of the present invention to provide packaging materials and Packaging Articles formed therefrom comprising a regio-regular, linear hydrocarbon polymer having a structure comprising vicinal pendent functional groups uniformly distributed along the polymer chain.
It is a further object of the present invention to provide packaging materials and Packaging Articles formed therefrom having a structure composed of at least one layer wherein at least one of said layer(s) of the structure comprises a functionalized, linear, regio-regular hydrocarbon polymer.
It is still further an object of the present invention to provide packaging material and Packaging Articles formed therefrom having a structure composed of at least one layer wherein at least one of said layer(s) of the structure comprises a hydroxyl functionalized, linear, regio-regular hydrocarbon polymer and, preferably wherein the hydroxyl groups are pendent from vicinal carbon atoms of the polymer chain.
It is further an object of the present invention to provide packaging material and Packaging Articles formed therefrom which are capable of exhibiting very low degrees of gas (e.g., oxygen) permeability and are capable of having said low permeability irrespective of environmental moisture content.